Silica-thickened grease containing carbamate ester stabilizer



Patented .iaa. 19, 1960 SlLICA-THICKENED GREASE CONTAINING CARBAMATE ESTER STABILIZER Nathaniel L. Remes, Miami, Fla, and Thomas W. Martinek and Ernest T. Fronczak, Crystal Lake, 11]., assignors to The Pure Oil Company, Chicago, 115., a corporation of Ohio N0 Drawing. Application December 24, 1957 Serial No. 704,892

15 Claims. (Cl. 252-28) This invention relates to new and useful improvements in grease compositions and more particularly to a silicathickened grease utilizing an improved dispersant for the silica gelling agent.

This invention is based upon our discovery that the esters of carbamic acid and substituted carbamic acids are superior dispersants for silica-thickened greases. This invention is further based upon our discovery that certain of the carhamate esters are not only useful as dispersants for silica-thickened greases but also prevent separation of the silica from the grease upon contact with water.

Although, the classical definition of lubricating greases is restricted to oils which are thickened or gelled with soaps, there has been developed a number of grease-like lubricants which are based upon synthetic lubricating liquids other than oil, or which utilize gelling or thickening agents other than soaps, but which are recognized as greases. In fact, non-soap-thickened greases have been given considerable attention in recent years for high-temperature applications, since these greases do not melt at elevated temperatures. These greases are discussed at considerable length in Manufacture and Application of Lubricating Greases, Boner, Reinhold, 1954. The nonsoap-thickened greases differ very substantiallyv from the soap-thickened greases and differ among themselves to a very great extent. For example, the non-soap-thickened greases generally are less susceptible to bleeding and to change of consistency on increase of temperature. Bentone greases are thermally stable and mildly resistant to Water. On the other hand, silica-thickened greases are thermally stable but decompose readily upon contact with water unless waterproofing agents are used which prevent separation of the silica particles from the oil. Additives which are used' for various purposes in connection with the soap-thickened greases are quite variable in their effect on the various non-soap-thickened greases. For example, metal carbamates and thiocarbamates which are reported (in U.S. Patents 2,652,362 and 2,652,363) to be useful as corrosion inhibitors and stabilizers for soap-thickened greases are completely ineffective as stabilizers for bentone and silica-thickened greases. Butyl stearate and coconut oil are each reported (in U.S. Patent 2,662,058) to be useful as dispersion aids for bentone greases but have been found to be completely ineffective as dispersants for silica-thickened greases. These variations in effect of stabilizers and dispersants for soapthickened and non-soap-thickened greases indicate the hi hly empirical nature of the grease-making art in general and the art of making non-soap-thickened greases in particular.

It is therefore one object of this invention to provide a new and improved silica-thickened grease of high yield.

Another object of this invention is to provide a new and improved silica-thickened grease containing a dispersant for the silica which also prevents destruction of the grease upon contact with water.

A feature of this invention is the provision of an im= proved silica-thickened grease which utilizes esters of carbamic acid and substituted carbamic acids as dispersants.

Another feature of this invention is the provision of an improved silica-thickened grease which uses a carbamate ester as a dispersant for the silica, which ester also functions to maintain the silica particles in a grease structure in the presence of small amounts of water.

Other objects and features of this invention will become apparent from time to time throughout the specification and claims as hereinafter related.

In carrying out this invention, silica-thickened greases are prepared by dispersing in a mineral oil about 5 to 15% by weight of finely-divided silica. The silica is dispersed, together with 0.25 to 2.25% by weight of a carbamate ester of the formula,

R1NC0R3 (or polymers or condensed forms thereof), where R, and R are of the group consisting of hydrogen, and alkyl, aryl, arylalkyl, and alkylaryl groups containing 1 to 24 carbon atoms, and R is of a group consisting of alkyl,

aryl, alkylaryl, and arylalkyl groups containing from IV to 24 carbon atoms and derivatives thereof, such as.- In the case of esters in which. of l to 3 carbon atoms, it is: necessary to include about 0.25 to 2.25 by weight of.

monohydroxy derivatives. the R is an alkyl group a polyalkylene glycol waterproofing agent, Ucon LB550X,. a polyalkylene glycol produced by the reaction of butanol'. and 1,2-propylene oxide, of high molecular weight (e.g.,; about 1400). When the group R contains from 4 to 24 carbon atoms the ester is water-insoluble and functions as a water-proofing agent for the silica particles as Well as a dispersant therefor.

In order to demonstrate this invention, several grease compositions were prepared to provide comparison between the improved grease of this invention and other grease compositions.

EXAMPLE I A conventional grease-making kettle was charged with 91.2 parts by Weight of vis. bright stock and 0.8 part by weight of n-butyl carbamate (NH C(O)OC H The mixture was thoroughly agitated and heated to 205 F. To this mixture there was added 8.0 parts by weight of finely divided amorphous silica, marketed under the trade name Cab-O-Sil. Cab-O-Sil is a finely-divided silica produced by high-temperature, vapor-phase hydrolysis of silicon tetrachloride. The agitation of the mixture was continued during addition of the silica gelling agent and the mixture was further agitated and maintained at 190205 F. for a period of about 90 minutes. The material was then charged to a colloid mill with a rotor-stator clearance of 0.003", and was milled at a flowrate of 0.60.7 pound per minute. The grease thus produced was then allowed to cool and was tested using a standard cone-penetration test. The grease had a worked penetration of 236, which is a NLGI #3 grease. This grease is stable and the silica does not settle out upon contact with water.

XAMPLE II added 8.0 parts by Weight of finely divided Cab-O-Sil silica. The agitation of the mixture was continued during the addition of the silica and the mixture was agitated and maintained at 190 205 F for a period of about 90 minutes. The grease was then charged to a colloid mill with a'rotor-stator clearance of 0.03, and was milled at a fiow rate of 0.6-0.7 pound per minute. The grease was then allowed to cool and was tested using a standard cone penetration test. This grease had an unworked penetration of 261 and a worked penetration of 263, corresponding to a #2 grease. The narrow range of worked and unworked penetration indicates a very high shear stability for this grease. 'This grease, however, is limited in application to essentially anhydrous conditions since it is decomposed upon contact with water. When this grease. is compounded using an equal amount of carbainate ester and a polyalkylene glycol waterproofing agent. (such as Ucon LB 550X), the grease is rendered stable to water without appreciable. change in yield or hardness.

EXAMPLE III In still another experiment a grease was compounded, using the procedure set forth in Examples I and H, from 91.2 parts by Weight of 160 vis. bright stock, 0.8 part by weight of ethyl carbamate, and 8.0 parts by weight of Cab-O-Sil silica. The grease produced from these ingredients had an unworked penetration of 234 and a worked penetration of 245, corresponding to a #3 grease. The narrow range of unworked and worked penetrations indicates good shear stability for the grease. This grease is very stable at elevated temperatures but becomes grainy after contact with large amounts of water. When 0.8 part by weight of Ucon LBSSOX, a polyalkylene glycol produced by reaction of butanol and 1,2-propylene oxide and having an average molecular weight of about i 1400, is added tothis grease composition there is produced a stable grease from which the silica does not settle upon contact with water.

EXAMPLE IV In several other experiments greases were compounded, using the procedure of Examples I to III, composed of 91.2 parts by Weight lubricating oil, 8.0 parts by weight Cab-O-Sil silica, and 0.8 part by weight carbamate ester dispersant. In Table I the particular ester used in each grease composition is identified and also the consistency of the resulting grease.

Oarbamate ester:

4-ethyl N,\ -dibut l carbamate. 5-2-hydroxyethyl N-hexadecyl carbamate. 6ethyl N-hexadecyl carbamate.

7ethyl N-p-ehlorophenyl carbarn ate.

8et'n vl N-3-(dim ethylarnino)-propyl-carbamute. Si-bis-ethyl hexamethylene-carbamate.

10dodecy1 carbamate. 11phenyl carbamate.

Grease No. Grease No. Grease N 0. Grease No. Grease No. Grease No.

, Grease No. Grease No. Lubricating oil:

Greases Nos. 4 to 9-160 vis. bright stock. Greases Nos. 10 t0 1l85 VI. 150 vis. bright stock.

EXAMPLE V In still another experiment an attempt was made to prepare silica-thickened grease using zinc dibutyl dithiocarbamate as a dispersant for the silica. In this experiment the dispersant, oil, and silica were charged to a grease-processing kettle, and heated and agitated in the same manner as in Examples I to H1. The mixture charged consisted of 91.2 parts by weight of 160 vis. bright stock, 8.0 parts by weight of Cab-O-Sil silica, and'0.8 part by Weight of Zinc dibutyl dithiocarbamate. The product obtained from these ingredients was completely. fluid and not a grease.

From these and other experiments it has been estabwhere R and R are of the group consisting of hydrogen and alkyl, aryl, arylalkyl, and alkylaryl groups containing 1 to 24 carbon atoms, and R is of the group consisting of alkyl, aryl, alkylaryl, and arylalkyl groups containing l to 24 carbon atoms and derivatives thereof, such as the monohydroxy and amino derivatives. When the ester group R contains 4 or more carbon atoms and is water-insoluble, it functions as a waterproofing agent for the grease as well as a dispersant for stablizing the grease. Examples of carbamate esters which are useful as dispersants for silica-thickened greases are: ethyl carbamate, propyl carbamate, butyl carbamate, hexyl carbamate, octyl carbamate, dodecyl carbamate, hexadecyl carbamate, eicosyl carbamate, phenyl carbamate, naphthyl carbamate, cresyl carbamate, phenylethyl carbamate, phenylbutyl carbamate, hydroxyethyl carbamate, 4-hydroxybutyl carbamate, Z-hydrQXyethyl-N-methyl carbamate, butyl-N-methyl carbamate, hexyl-N, N-dimethyl carbamate, amyl-N-ethyl carbamate, benzyl-N-rnethyl carbamate, etc. These carbamates are generally operative asdispersants for silica-thickened grease when added to the grease composition at a concentration of 0.25 to 2.25% by weight.

While there have been described several preferred embodimentsof this invention, including several specific examples of the best mode of carrying out this invention, it should be understood that within the scope of the appended claims this invention maybe practiced otherwise than as specifically described.

What is claimed is:

1. A lubricating grease consisting essentially of a major portion of a lubricating oil having incorporated therein a small amount of finely divided silica sufficient to produce a gel-like grease structure, and a carbamate ester of the formula where R and R are of the group consisting of hydrogen and alkyl, aryl, alkylaryl, and arylalkyl groups containing 1 to 24 carbon atoms, and R is of the group consisting of alkyl, aryl, alkylaryl, and arylalkyl groups containing 1 to 24 carbon atoms and monohydroxy derivatives thereof, in an amount sufiicient to effect a complete and stable dispersion of the silica.

2. A grease according to claim 1 in which the ester is present in the amount of 0.25 to 2.25% by weight.

3. A grease according to claim 1 in which the ester is waterinsoluble and is of the formula where R and R are of the group consisting of hydrogen and alkyl, aryl, alkylaryl, and arylalkyl groups containing 1 to 24 carbon atoms, and R is of the group consisting of alkyl, aryl, alkylaryl, and arylalkyl groups containing 4 to 24 carbon atoms and monohydroxy derivatives thereof.

4. A grease according to claim 1 in which the silica used is an amorphous silica of very fine particle size produced by a high-temperature, vapor-phase reaction of a siliceous material.

5'. A lubricating grease consisting essentially of a major portion of a petroleum lubricating oil having incorporated therein about 5 to 15% by weight of an amorphous silica of very fine particle size, and 0.25- 2.25% by weight of a dispersing agent for the silica consisting of a carbamate ester of the formula where R, and R are of the group consisting of hydrogen and alkyl, aryl, alkylaryl, and arylalkyl groups containing 1 to 24 carbon atoms, and R is of the group consisting of alkyl, aryl, alkylaryl, and arylalkyl groups containing 1 to 24 carbon atoms and monohydroxy derivaatives thereof.

6. A grease according to claim 5 in which the carbamate ester is n-butyl carbamate.

7. A grease according to claim 5 in which the carbamate ester is ethyl carbamate and the grease includes from 0.25% to 2.25%

waterproofing agent.

8. A grease according to claim 5 is which the carbamate ester is 2-hydroxyethyl-N-methy1 carbamate, and

by weight of a polyalkylene glycol the grease includes from 0.25 to 2.25% polyalkylene glycol waterproofing agent.

9. A grease according to claim 5 in which the ester is ethyl N,N-dibutyl carbamate.

10. A grease according to claim 5 in which the ester is ethyl N-hexadecyl carbamate.

11. A grease according to claim 5 in which the ester is ethyl N-p-chlorophenyl carbamate.

12. A grease according to claim 5 in which the ester is ethyl N-3-(dimethylamino)-propyl-carbamate.

13. A grease according to claim 5 in which the ester is bis-ethyl hexamethylene-carbamate.

14. A grease according to claim 5 in which the ester is dodecyl carbamate.

15. A grease according to claim 5 in which the ester is phenyl carbamate.

References Cited in the file of this patent UNITED STATES PATENTS by weight of a 2,636,028 Sommer Apr. 21, 1953 2,640,822 Harman June 2, 1953 2,766,205 Marshall Oct. 9, 1956 

1. A LUBRICATING GREASE CONSISTING ESSENTIALLY OF A MAJOR PORTION OF A LUBRICATING OIL HAVING INCORPORATED THEREIN A SMALL AMOUNT OF FINELY DIVIDED SILICA SUFFICIENT TO PRODUCE A GEL-LIKE GREASE STRUCTURE, AND A CARBONATE ESTER OF THE FORMULA 